Motors in space and hardened applications can have environmental constraints, including radiation and thermal constrains, that place extreme demands on the motor. The size and weight of these motors are also taken into account, as the costs of weight and volume are important considerations for hardware that will be launched into space. Finally, since these motors are often part of complex instruments that make very sensitive measurements, the generation of minimal and predictable electromagnetic interference (EMI) is critical.
Sensorless motor controllers detect the position of the rotor in order to properly commutate the motor. One technique that can be used is called back electromotive force (EMF) sensing. The concept behind back EMF detection is that the position of a rotor can be detected by looking at the back EMF on windings within the motor. Current designs use a technique where the back EMF is measured in respect to a pseudo ground representing the actual neutral of the stator winding.
The speed of the motor is controlled as well. Typically this is accomplished by applying a pulse width modulation (PWM) pattern to either high side or low side field effect transistors (FETs), or both. This results in high power losses due to high frequency switching waveforms as well as wide-band frequency spectrum noise.
Furthermore, current sensorless motor designs are often bulky, and unsuitable for use in high-temperature and high-radiation applications, such as space-based applications. Motor placement in machines used for such applications is generally not conducive to shielding sensitive components from high temperature and radiation, and in some cases the motor or the device it drives operates at high temperatures. Many components currently used in motor control systems cannot withstand these types of operating conditions.